The invention relates to systems and methods for ablating myocardial tissue for the treatment of cardiac conditions.
Normal sinus rhythm of the heart begins with the sinoatrial node (or xe2x80x9cSA nodexe2x80x9d) generating an electrical impulse. The impulse usually propagates uniformly across the right and left atria and the atrial septum to the atrioventricular node (or xe2x80x9cAV nodexe2x80x9d). This propagation causes the atria to contract.
The AV node regulates the propagation delay to the atrioventricular bundle (or xe2x80x9cHISxe2x80x9d bundle). This coordination of the electrical activity of the heart causes atrial systole during ventricular diastole. This, in turn, improves the mechanical function of the heart.
Today, as many as 3 million Americans experience atrial fibrillation and atrial flutter. These people experience an unpleasant, irregular heart beat, called arrhythmia. Because of a loss of atrioventricular synchrony, these people also suffer the consequences of impaired hemodynamics and loss of cardiac efficiency. They are more at risk of stroke and other thromboembolic complications because of loss of effective contraction and atrial stasis.
Treatment is available for atrial fibrillation and atrial flutter. Still, the treatment is far from perfect.
For example, certain antiarrhythmic drugs, like quinidine and procainamide, can reduce both the incidence and the duration of atrial fibrillation episodes. Yet, these drugs often fail to maintain sinus rhythm in the patient.
Cardioactive drugs, like digitalis, Beta blockers, and calcium channel blockers, can also be given to control the ventricular response. However, many people are intolerant to such drugs.
Anticoagulant therapy also combats thromboembolic complications.
Still, these pharmacologic remedies often do not remedy the subjective symptoms associated with an irregular heartbeat. They also do not restore cardiac hemodynamics to normal and remove the risk of thromboembolism.
Many believe that the only way to really treat all three detrimental results of atrial fibrillation and flutter is to actively interrupt all the potential pathways for atrial reentry circuits.
James L. Cox, M.D. and his colleagues at Washington University (St. Louis, Mo.) have pioneered an open heart surgical procedure for treating atrial fibrillation, called the xe2x80x9cmaze procedure.xe2x80x9d The procedure makes a prescribed pattern of incisions to anatomically create a convoluted path, or maze, for electrical propagation within the left and right atria, therefore its name. The incisions direct the electrical impulse from the SA node along a specified route through all regions of both atria, causing uniform contraction required for normal atrial transport function. The incisions finally direct the impulse to the AV node to activate the ventricles, restoring normal atrioventricular synchrony. The incisions are also carefully placed to interrupt the conduction routes of the most common reentry circuits.
The maze procedure has been found very effective in curing atrial fibrillation. Yet, despite its considerable clinical success, the maze procedure is technically difficult to do. It requires open heart surgery and is very expensive. Because of these factors, only a few maze procedures are done each year.
It is believed the treatment of atrial fibrillation and flutter requires the formation of long, thin lesions of different lengths and curvilinear shapes in heart tissue. Such long, thin lesion patterns require the deployment within the heart of flexible ablating elements having multiple ablating regions. The formation of these lesions by ablation can provide the same therapeutic benefits that the complex incision patterns that the surgical maze procedure presently provides, but without invasive, open heart surgery.
With larger and/or longer multiple electrode elements comes the demand for more precise control of the ablating process. The delivery of ablating energy must be governed to avoid incidences of tissue damage and coagulum formation. The delivery of ablating energy must also be carefully controlled to assure the formation of uniform and continuous lesions, without hot spots and gaps forming in the ablated tissue.
The task is made more difficult because heart chambers vary in size from individual to individual. They also vary according to the condition of the patient. One common effect of heart disease is the enlargement of the heart chambers. For example, in a heart experiencing atrial fibrillation, the size of the atrium can be up to three times that of a normal atrium.
One objective of the invention is to provide tissue ablation systems and methods providing beneficial therapeutic results without requiring invasive surgical procedures.
Another objective of the invention is to provide systems and methods that simplify the creation of complex lesions patterns in body tissue, such as in the heart.
A principal objective of the invention is to provide improved structures and methodologies for deploying electrode elements in contact with tissue. In a preferred implementation, the structures and methodologies that embody features of the invention make possible the creation of long, thin lesion patterns in tissue for the treatment of, for example, heart conditions like atrial fibrillation or atrial flutter.
In achieving these objectives, the invention provides an electrode support structure comprising a guide body having at its distal end a flexible spline leg. The spline leg is flexed to define an arcuate shape to facilitate intimate contact against tissue. An electrode element is carried by the spline leg for movement along its axis. The structure includes a control element coupled to the electrode element. The control element remotely imparts force to move the electrode element along the axis of the spline leg. Therefore, in use, the physician can cause the electrode element to travel along a path that the spline leg defines, without otherwise changing the location of the guide body.
The invention also provides a method for ablating tissue in a heart. The method introduces a probe into the heart. The probe carries at least one elongated spline leg flexed outward of the probe to define an arcuate shape. The probe also includes at least one ablation electrode that is movable along the at least one spline leg spline in response to the application of force. The method establishes contact between the ablation electrode and a region of heart tissue, along which the spline leg defines an elongated path. The method transmits ablation energy to the ablation electrode while in contact with the tissue region. The method also applies force to move the ablation electrode along the at least one spline leg, while maintaining contact with the tissue, to ablate tissue along the elongated path.
Other features and advantages of the inventions are set forth in the following Description and Drawings, as well as in the appended Claims.